A compound semiconductor crystal such as GaAs has been made use of in various industrial fields, and for example, made use of as a material for a semiconductor device such as an electronic device or an optical device. In order to lower cost for manufacturing a semiconductor device, increase in diameter of a substrate made use of for a semiconductor device, improvement in manufacturing yield of a semiconductor device, or improvement in performance of a semiconductor device is essential. To that end, a substrate of which crystal quality is stable and ensured is required.
For example, Japanese Patent Laying-Open No. 5-339100 (PTD 1) discloses a compound semiconductor single crystal of which average value of residual strain in a crystal is not greater than 1×10−5. According to this document, a semiconductor device is manufactured with the use of a compound semiconductor single crystal substrate composed of such a compound semiconductor single crystal, so that occurrence of crystal defects (for example, slip) in an epi layer can significantly be suppressed during epitaxial growth and a process of a device, and a semiconductor device of high performance can be manufactured at high yield.
Japanese Patent Laying-Open No. 2008-239480 (PTD 2) discloses a GaAs single crystal having an average dislocation density not lower than 1×103 cm−2 and not higher than 1×104 cm−2. This document describes manufacturing of a GaAs substrate made use of for an optical device or an electronic device by using the GaAs single crystal.